In a typical cellular network, also referred to as a wireless communication system, User Equipments (UEs), communicate via a Radio Access Network (RAN) to one or more Core Networks (CNs).
A user equipment is a mobile terminal by which a subscriber may access services offered by an operator's core network and services outside the operator's network to which the operator's radio access network and core network provide access. The user equipment may be for example a communication device such as mobile telephone, cellular telephone, smart phone, tablet computer, Machine to Machine (M2M) device or laptop with wireless capability. The user equipment may be portable, pocket storable, hand held, computer comprised, or a vehicle mounted mobile device, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another mobile station or a server. The user equipment is enabled to communicate wirelessly in the communication network. The communication may be performed e.g. between two user equipments, between a user equipment and a regular telephone and/or between the user equipment and a server via the radio access network and possibly one or more core networks, comprised within the communication network.
The radio access network covers a geographical area which is divided into cell areas. Each cell area is served by a Base Station (BS), e.g. a Radio Base Station (RBS), which in some radio access networks is also called evolved NodeB (eNB), NodeB or B node. A cell is a geographical area where radio coverage is provided by the radio base station at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipments within range of the base stations.
A user equipment that does not follow the third Generation Partnership Project (3GPP) standard may end up in an eternal signaling loop consuming radio access network and core network resources, beside the fact that they never get service until a manual power cycle or a Denial-Of-Service attack (DOS) occurs.
In GERAN/UTRAN, a Routing Area Update (RAU) procedure is used to update the Routing Area (RA) of the user equipment when the user equipment moves from one routing area to another. In Long Term Evolution (LTE), the corresponding procedure is Tracking Area Update (TAU). The user equipment initiates TAU when it detects that it enters a new Tracking Area (TA). The routing area or tracking area is a geographical area within a Public Land Mobile Network (PLMN). When the RAU cannot be accepted, the network sends a RAU Reject message to the user equipment. The RAU Reject message comprises a Cause Code (CC) value indicating the cause of the rejection. For example, from an operator perspective some user equipments seem to be difficult when receiving the RAU Reject message comprising the error cause indicator CC#17. The CC#17 in the RAU Reject message indicates that the cause of the rejection is a network failure. This is similar for the TAU procedure. GERAN is short for GSM EDGE Radio Access Network, GSM is short for Global System for Mobile Communications and EDGE is short for Enhanced Data rates for GSM Evolution. UTRAN is an abbreviation for Universal Terrestrial Radio Access Network.
Considering the following example data traffic scenario:                1) The user equipment performs Inter Radio Access Technology (IRAT) mobility by moving from 2G to 3G, i.e. from GSM to WCDMA.        2) The user equipment is rejected by the Serving General packet radio service Support Node (SGSN) with a CC#17 message. There may be many different reasons to why the SGSN rejects the user equipment with a CC#17.        
When scenario 1) or 2) happens, the user equipment will not re-attach, instead it will be looping by sending another RAU Request to the SGSN and receiving a RAU Reject CC#17 from the SGSN again. IRAT mobility, as mentioned above, refers to mobility of a user equipment between LTE and earlier 3GPP technologies.
FIG. 1a illustrates a current example of a RAU procedure. The RAU procedure is initiated by the user equipment when it leaves one routing area and enters another. FIG. 1a illustrates a communication network 100a comprising a SGSN 101a, a Domain Name System (DNS) server 105a and a user equipment 110a. The user equipment 110a has moved from one routing area to another routing area. The SGSN 101a is responsible for delivery of data packets to and from the user equipment(s) within its geographical service area. The tasks of the SGSN 101a comprise packet routing and transfer, mobility management (attach/detach and location management), logical link management, and authentication and charging functions. The SGSN 101a stores location information and user profiles of all General Packet Radio Service (GPRS) user equipments 110a registered with the SGSN 101a. Simplified, the DNS 105a is an internet service that connects domain names to Internet Protocol (IP) addresses, i.e. it translates the domain names into IP addresses. The RAU procedure exemplified in FIG. 1a comprises the following steps, which steps may be performed in any suitable order:
Step 111a 
The user equipment 110a sends a RAU Request to the SGSN 101a when it leaves one routing area and enters another. A change from an old SGSN to the SGSN 101a also occurs.
Step 112a 
The SGSN 101a receives the RAU Request and sends a DNS query to the DNS 105a in order to find a cooperating old SGSN. The term old used together with the SGSN refers to the SGSN located in the previous routing area from which the user equipment 110a has moved.
Step 113a 
The DNS 105a receives the DNS query from the SGSN 101a and translates it into an IP address for the purpose of locating the co-operating SGSN. By some reason, the DNS 105a does not find the co-operating old SGSN, and therefore sends a DNS return error back to the SGSN 101a. 
Step 114a 
The SGSN 101a receives the DNS return error from the DNS 105a and sends a RAU Reject with the cause code CC#17 indicating a network failure back to the user equipment 110a. The RAU Reject CC#17 causes the user equipment 110a to go back to step 111a and to send a new RAU Request. Thus, the user equipment 110a is stuck in a loop of sending a RAU Request and receiving a RAU Reject. The information retrieved from the DNS 105a may be locally configured in the SGSN 101a. 
FIG. 2a illustrates another example of a communication network 200a and a Packet Data Protocol (PDP) procedure. The communication network 200a comprises the user equipment 110a, the SGSN 101a and a Gateway GPRS Support Node (GGSN) 207a. The GGSN 207a is responsible for the interworking between the GPRS network and external Packet Switched (PS) networks. The GGSN 207a has a record comprising information of active user equipments and the SGSNs to which the user equipments are attached, whereof one user equipment is the user equipment 110a. The GGSN 207a allocates IP addresses to user equipment 110a and is responsible for billing.
PDP is a packet transfer protocol used in communication networks. A PDP context is a term indicating a logical associated between the user equipment 110a and a Public Data Network (PDN) running across a GPRS network. A PDP context activation may be initiated by the user equipment 110a or it may be requested by the network. After a PDP context activation, the user equipment 110a may send IP packets over the air interface to the base station. The user equipment 110a may have several active PDP contexts at the same time.
The PDP procedure exemplified in FIG. 2a comprises the following steps, which steps may be performed in any suitable order:
Step 211a 
The user equipment 110a sends a service request to the SGSN 101a. The service request is sent for example because the user equipment 110a has pending uplink signaling. A signaling connection is established between the user equipment 110a and the SGSN 101a as a result of the service request.
Step 212a 
The user equipment 110a sends an Activate PDP Context request to the SGSN 101a in order to activate a PDP context. The Activate PDP Context changes a session management state to active.
Step 213a 
The SGSN 101a receives the Activate PDP Context request from the user equipment 110a and sends a Create PDP Context Request to the GGSN 207a. 
Step 214a 
The GGSN 207a receives and examines the Create PDP Context Request. As mentioned above, the GGSN is responsible for billing and may therefore be able to perform a credit control for user equipment 110a, i.e. subscriber. If the credit control performed by the GGSN 207a detected that there is no money left on an account associated with the user equipment 110a, the GGSN 207a sends a Create PDP Context Response to the SGSN 101a indicating that the failure is due to that there is no money left.
Step 215a 
The SGSN 101a receives the Create PDP Context Response from the GGSN 207a and sends an Activate PDP Context Reject back to the user equipment 110a. The procedure the goes back to step 211a, i.e. user equipment 110a is stuck in the loop.
FIG. 3a illustrates another example of a communication network 300a and a PDP procedure. The communication network 300a comprises the user equipment 110a and the SGSN 101a. The procedure comprises the following steps, which steps may be performed in any suitable order:
Step 311a 
The user equipment 110a sends a service request to the SGSN 101a. The service request is sent for example because the user equipment 110a has pending uplink signaling. A signaling connection is established between the user equipment 110a and the SGSN 101a as a result of the service request.
Step 312a 
The user equipment 110a sends an Activate PDP Context request to the SGSN 101a in order to activate a PDP context. The Activate PDP Context changes the session management state to active.
Step 313a 
The SGSN 101a receives the Activate PDP Context request from the user equipment 110a and checks whether the Access Point Name (APN) exist. APN allows the user equipment 110a to access the Internet. The APN may be seen as a name (web address) of an access point or gateway towards Internet. In this example, the SGSN 101a determines that the APN does not exist.
Step 314a 
When the SGSN 101a has determined that the APN does not exist, it sends an Activate PDP Context Reject to the user equipment 110a. This causes the user equipment 110a to go back to step 311a, i.e. it is stuck in the loop of sending a request and receiving a rejection.
As described in the examples in FIGS. 1a, 2a and 3a, the user equipment is stuck in the loop of sending a request and receiving a rejection. Thus, the user equipment 110a consumes unnecessary radio access network resources and an unnecessary amount of signaling is transmitted in the network.